Contactless chip cards communicate without using electrical connections to reading and writing terminals. In passive chip cards, the power required for communication and for data processing is provided by the terminal in the form of an electromagnetic field by means of a terminal antenna. The electromagnetic field is coupled to the chip card by means of an antenna on the chip card.
FIG. 1 shows a conventional rectifier and voltage regulator circuit. The voltage induced in a chip card antenna is applied at a first input A1 and a second input A2 and is rectified by a rectifier R. The rectified voltage VR is smoothed by means of a reservoir capacitor CR. A series voltage regulator SR is used to regulate the output voltage VDD for an electric chip L of the chip card.
Usually, load modulation is used for transmitting data from the chip card to the terminal by changing the electrical load on the chip card antenna in a way that depends on the data that is to be transmitted. Since the chip card antenna is coupled to the terminal antenna by means of an electromagnetic field, these load changes also affect the voltage at the terminal antenna. The resultant voltage changes correspond to the transmitted data and can be demodulated to obtain the transmitted data.
A challenge in producing contactless chip cards is to reduce their cost and to improve their technical performance characteristics.